1. Field of the Invention
The invention relates to surgical scissors instruments and, more particularly, to endoscopic scissor instruments having small-sized scissor blades.
2. State of the Art
Endoscopy is a minimally invasive diagnostic medical procedure that is used to assess the interior of the human body using an endoscope. An endoscope generally consists of a rigid or flexible tube, an fiber optic illumination system to guide light provided by a light source through the tube of the endoscope in order to illuminate the organ or object under inspection, and a viewing system for collecting an image of the organ or object under inspection and for recording the image on an internal CCD device (video-endoscope) or for transmitting the image through the tube via a fiber optic bundle to an external video processor for viewing (fiber-endoscope). The endoscope can include one or more “operating” channels (typically 2-4 mm in diameter) that provide for passage of specialized medical instruments through the endoscope and into the field of view. Such specialized instruments (which can include biopsy forceps, brushes, needles, snares, scissors, graspers, cutters, clip appliers, etc.) can be used to take biopsies and retrieve organs (or pieces thereof) and/or foreign objects from the inside of the body. In some instruments (especially those with lateral-viewing optics), the distal tip of the operating channel incorporates a small deflectable elevator or bridge, which permits some directional control over the instrument exiting therefrom. These general principles apply to most endoscopes, but specific instruments differ in length, size, stiffness, as well as other characteristics as the instruments are typically designed for a particular application. Endoscopy can involve, for example, the gastrointestinal tract such as the esophagus, stomach and duodenum, small intestine, and colon. It can also involve the respiratory tract, the urinary tract, the female reproductive system, and the organs of the chest. It can also involve the interior of a joint (arthroscopy). Many endoscopic procedures are considered to be relatively painless and, at worst, associated with moderate discomfort.
Laparoscopy is a minimally invasive surgical technique in which operations in the abdomen or thorax are performed through small incisions (usually 0.5-1.5 cm) via a laparoscope. There are generally two types of laparoscopes, including a telescopic rod lens system that is usually connected to a video camera (single chip or three chip) and a digital laparoscope where the camera is placed at the end of the laparoscope, thus eliminating the rod lens system. A fiber optic cable system connected to a light source (halogen or xenon is inserted through a surgical port to illuminate the operative field for viewing. The abdomen is usually insufflated with carbon dioxide gas to create a working and viewing space. Specialized surgical instruments can be introduced into the abdomen or thorax through a surgical port in order to take biopsies and retrieve organs (or pieces thereof) and/or foreign objects from the inside of the body.
The specialized surgical instruments used for endoscopy, laparoscopy or arthroscopy generally include end effector means (e.g., graspers, cutters, forceps, scissors, clip appliers, etc.) mounted adjacent the distal end of a tube or coil. Handles (or other actuation control means) are mounted to the proximal end of the tube or coil and move an actuator axially through the tube or coil. The distal end of the actuator is mechanically coupled to the end effector means in a manner that transforms the axial movement of the actuator into the desired movement of the end effector means. Such specialized endoscopic, laparoscopic or arthroscopic surgical instruments are collectively referred to herein as endoscopic surgical instruments or endoscopic instruments. These general principles apply to most endoscopic instruments, but specific endoscopic instruments differ in length, size, stiffness, as well as other characteristics as the instruments are typically designed for a particular application as such instruments can be used for a wide variety of minimally invasive surgical procedures, including the endoscopic, laparoscopic and arthroscopic applications summarized above.
Endoscopic surgical scissors instruments generally include a pair of scissor blades pivotably mounted adjacent the distal end of a tube or coil. The scissor blades have sharpened edges that effect cutting of tissue during pivotal movement of the scissor blades relative to one another. Handles (or other actuation control means) are mounted to the proximal end of the tube or coil and move an actuator axially through the tube or coil. The distal end of the actuator is mechanically coupled to the scissor blades in a manner that transforms the axial movement of the actuator into pivoting movement of the scissor blades.
Endoscopic scissors instruments may be generally classified as either “single acting” or “double acting.” In a single acting instrument, a stationary scissor blade is supported adjacent the distal end of the tube or coil and a movable scissor blade is coupled to the distal end of the actuator and is supported adjacent the distal end of the tube or coil for rotation relative to the stationary scissor blade in accordance with actuation transmitted by the actuator. In double acting instruments, two scissor blades are coupled to the distal end of the actuator and supported adjacent the distal end of the tube or coil for rotation relative to one another in accordance with actuation transmitted by the actuator.
The construction of the scissor blades theoretically supplies a moving contact point between the opposing cutting edges as the scissor blades are closed by their pivotable movement. In order to effect a smooth cutting action, the engaging cutting edges must be kept in a moving contact point throughout the closing of the scissor blades. Typical scissor designs usually accomplish this by the use of any of the following methods: firstly, via a mechanism or feature separated from the blades that biases the scissor blades together as the scissor blades are closed; secondly, by dimensioning the blades with a longitudinally bowed profile that forces the opposed scissor blades against each other as the scissor blades are closed and lastly by a very accurately constructed assembly with no mechanical slop in the dimensions of, or the positioning of, the scissors' blades or related components
The biasing means of the first example typically is accomplished by tightening the scissors' pivot nut to remove all dimensional slop in the assembly or with a cammed surface behind the pivot area that effects biasing of the scissor blades closer together as they close over each other. In the second method, which is used most commonly for larger or longer scissor blades, such as those in a standard full-sized scissor as used in regular “open” surgery, a bowed-profile that runs along the longitudinal axis of the scissor blade forces the cutting edges together. This method gives a mostly adequate cutting performance for open style surgical scissors. However for smaller scissor blades such as those used in endoscopic devices, the total loss of resiliency, due to the stiffness of small blades, means that a bowed profile in the scissor blade will not work and will only result in the contacting cutting edges gouging each other or quickly wearing away. Therefore in the currently available endoscopic scissor devices such small non-resilient and rigid blades must be designed to maintain the edge to edge contact through the use of components with very stringent dimensional accuracies, tight tolerances and tight fits. This last design method involves difficult and costly assembly and manufacturing processes. In addition, the effects of using cams or similar features in the design of small endoscopic scissors is limited by the remoteness of the cam surface from the cutting edges and because of persistent assembly “slop” offers little improvement to the problem of maintaining edge to edge contact. These design schemes have historically failed to give small surgical scissor instruments the desired sensitive feel and cutting performance that surgeons require and are familiar with through their experience in open surgery using larger hand-held surgical scissors.